This invention relates particularly to overhead conveyors as are used to deliver, or in some cases to remove, materials from high places such as roof tops. In particular, the invention applies to such conveyors which are mobile, i.e. vehicle mounted, and may be part of a delivery truck for transporting materials such as roofing shingles. The truck is driven into a site where roofing or the like is to be applied or repaired, and the conveyor is positioned as to its elevation and azimuth using its own power drive equipment.
A major problem with such conveyor systems is the danger presented by nearby overhead electrical wires, which often are high tension lines in which the applied voltage may be anywhere from several kilovolts to several megavolts. Major accidents, with loss of life and/or severe injuries to operating personnel and destruction of equipment, occur when a metal overhead conveyor structure (e.g. boom) momentarily contacts this wiring.
Step ladders or extension ladders constructed of electrically non-conductive parts are available to workmen in lengths up to about 24 feet, but those are intended only for climbing and possibly carrying of small equipment or supplies, up to about 50 pounds in weight.
Heavy duty equipment, such as the mobile overhead conveyor systems, has traditionally been constructed of metal, and thus such equipment is highly susceptible to overhead wire accidents. Some of these accidents are so severe that the conveyor and its supporting truck is destroyed, with some of the heavy structural members being partially melted or distorted. The released electrical energy has been known to jump to adjacent vehicles and destroy or damage them also. Of course, any person in contact with this equipment at the time is subjected to a high electrical discharge, and if the person is fortunate enough to survive he is usually severely injured.
To minimize this type of accident, there is a need for electrically non-conductive overhead conveyor equipment which is robust enough to withstand heavy usage and large forces.